Pluto is a planet once again

[In case it wasn’t obvious: April Fool! -Ed.]

In a surprising reversal this week, members of the International Astronomical Union voted to reinstate Pluto’s status as a planet. This overturns the IAU’s 2006 decision to reclassify Pluto as a ‘dwarf planet’ following the adoption of an official definition of what constitutes a planet, which excluded Pluto.

Speaking on behalf of the IAU, one member is quoted as saying, “People were surprisingly passionate about Pluto’s status. The pressure from the general public to re-admit it to the ‘planet club’ was so great, we just couldn’t ignore it. Welcome back, Pluto.”

Just kidding. April Fool!

(Sorry, Pluto, you’re still a dwarf planet.)

18 thoughts on “Pluto is a planet once again

  1. Heh.

    As an astronomer, I’m sympathetic to the reasoning for reclassifying Pluto. It was either that or admit hundreds of new planets to the family.

  2. I was just bummed out when Pluto was “downgraded”, but very happy that they didn’t do so while the person who discovered it was still alive.

    The story how Clyde Tombaugh discovered the Lil’ Guy in 1930 is pretty darn inspiring.

  3. Oh no, nothing to do with science, but rather the fact that many scientists have no understanding the emotional attachments and subsequent emotional responses people have about the darnest things. Things like a small planet out on the edge of the solar system ignite passions.

    Notice I used an emotional word ‘miffed’, logic and science hasn’t much to do with it, but cultivating an hostile stance towards such things ends up with balkanized camps.

    And then it ends up looking like a scene from the classic monster movies :)

    In fact, today at lunch, my son was entertaining himself with a small coloring book that list eight planets. My gut reaction was “What about Pluto!?”, but I held my tongue. See? Humans do the craziest things!

  4. Pluto is still a planet, and that is no April Fool’s joke. Only four percent of the IAU voted on the controversial demotion, and most are not planetary scientists. Their decision was opposed in a formal petition by hundreds of professional astronomers led by New Horizons Principal Investigator Dr. Alan Stern. The IAU can claim whatever it wants, but its only “authority” derives from consensus, and such consensus does not exist among astronomer. Those who support a geophysical definition of planet reject the notion that an object must clear its orbit to be a planet and hold to a much broader definition, specifically, that a planet is any non-self-luminous spheroidal body orbiting a star. The spherical part is important because it means the object is large enough to be rounded by its own gravity, a characteristic of planets and not of shapeless asteroids. Significantly, Stern is the person who first coined the term dwarf planet, but he intended it to designate a third class of planets in addition to terrestrials and jovians–small planets large enough to be spherical but not large enough to gravitationally dominate their orbits. He never intended for dwarf planets to not be considered planets at all. I encourage you to check out my Pluto Blog at and Alan Boyle’s recent book “The Case for Pluto.” Don’t mourn Pluto–join those of us who reject the demotion!

  5. There are still plenty of books that include Pluto, and there are some new ones as well. I recommend you buy him “Ten Worlds” by Dr. Ken Croswell, and the brand new “Thirteen Planets,” a National Geographic book by David Aguilar. Both are appropriate for kids.

  6. What’s wrong with admitting hundreds of new planets? Astronomers have no problem with having billions of stars and billions of galaxies. The objection to “too many planets” is hardly scientific.

  7. Laurel, that’s interesting information, and thank you for sharing it.

    I understand why the IAU made the decision to demote Pluto, but put me in the “don’t really care either way” camp.

    You’re obviously very passionate and well-informed about this subject, so I wish you luck with your endeavor.

  8. There is nothing wrong with it. But I suspect for the voting members of the IAU — and to a small extent, me, personally — going from nine planets to hundreds of planets was too much of a paradigm shift compared with going from nine to eight.

  9. No, sorry, won’t do. Instead, I decided to become an astronomer myself and am now in a Masters program in astronomy and working on a book about Pluto. Just because a tiny minority of IAU members cannot deal with a shift from nine to hundreds of planets does not mean everyone else has to blindly follow. In fact, the IAU is not the only venue for such discussions and represents only one viewpoint in an ongoing controversy. I hope you will reconsider the paradigm shift to hundreds of planets because it’s actually very exciting.

  10. Thanks! I may be the only person in the solar system who changed her whole life because of Pluto, but it’s definitely been worth it! I’m curious as to what area of astronomy you specialize in, and I’m guessing you weren’t present for the IAU vote even if you are an IAU member (just because 96 percent of the members weren’t there). There have to be better ways of doing science that via the highly flawed, political process that went on in Prague.

  11. I am not a voting member of the IAU, and wasn’t present in Prague.

    My specialty is quasars, supermassive black holes, and galaxy evolution, which is probably why I’m not invested in the Pluto argument — my attention is focused billions of light-years away.

    Nevertheless, you’ve piqued my interest in the Pluto controversy. I’m curious whether it constitutes a genuine scientific battle as opposed to an argument over taxonomy. If you’re interested in providing a succinct explanation, I’d consider posting it on this blog.

    Not many people who believe strongly in something take a big step like you have (becoming an astronomer), so I commend you. Of course, I’m biased — I can’t imagine why anyone wouldn’t want to be an astronomer for a living. :)

  12. As a writer, I believe that semantics and systems of taxonomy matter. They inform the way we see the world and make sense of things. There is a taxonomy issue as to whether dwarf planets are or are not a subclass of planets, but this reflects a larger, scientific battle. That battle is between two ways of viewing the solar system, that of dynamicists and that of geophysicists. Even though I clearly support the latter, I wouldn’t say either way is wrong. Dynamicists focus on the interactions among celestial bodies. To them, what is important is whether and how a celestial body perturbs or interacts with other celestial bodies. Therefore, to them, the only significant objects are the largest ones in any particular orbit. They believe that to be considered a planet, an object must be the dominant object in its orbital zone (and not be a star). In contrast, geophysicists focus on individual celestial bodies themselves–their compositions, characteristics, etc.–rather than on the effects these objects have on other objects. To them, if an object orbits a star and is large enough to be rounded by its own gravity, it is a planet, whether or not it gravitationally dominates its orbit. One could say dynamicists give priority to where celestial objects are while geophysicists give priority to what these objects are.

    I commend you for choosing to study quasars, supermassive black holes, and galaxies. Not only are those more remote and abstract, to me, they are much more complicated and difficult to understand. As a writer, I tend to be stronger in verbal rather than math skills, and I find planetary science the least difficult of all branches of astronomy (that’s not to say it’s “easy” by any means). I’m not giving up writing and acting, but I’m definitely sticking with astronomy and am currently in the Masters program at Swinburne University. Currently, I’m taking time off to write a book “The Little Planet That Would Not Die: Pluto’s Story,” and I am as determined as ever to have a voice in the debate and see a broader definition of planet adopted.

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